Examples of buildings, which have a roof or walls formed of a transparent sheet or a transparent film, include houses for cultivating plants, barns, fish farming facilities, and sporting facilities. In such buildings, it is required to control the amount of light entering such buildings for various reasons. For example, some houses for cultivating plants are configured to allow as much light as possible to enter therein in the morning where plants actively photosynthesize while preventing an excessive amount of light from entering therein in the afternoon in order to reduce a temperature rise therein or the stress to plants.
As panels and buildings, which can control the amount of light entering buildings, the following proposals have been made:
1. A panel including two opposed transparent films, a frame holding these films in an airtight manner, and a vacuum pump and an air pump connected to the space surrounded by these films and the frame (see Patent Document 1)
2. A building having a roof and walls formed by a multiple sheet of a plurality of transparent sheet layers, and including a vapor supply system for supplying vapor in between opposed transparent sheet layers of the multiple sheet (see Patent Document 2)
In the panel mentioned in item 1, the vacuum pump reduces the pressure in the space between the two opposed transparent films to bring the two opposed transparent films into close contact with each other in order to increase the amount of light passing through the two opposed transparent films. However, the verification test conducted by the inventors of the present invention revealed that there was almost no change in the amount of light transmission between before and after bringing the two opposed transparent films into close contact with each other.
In the building mentioned in item 2, vapor is supplied in between the opposed transparent sheet layers of the multiple sheet to generate dew condensation on the opposed surfaces of the opposed transparent sheet layers in order to decrease the amount of light passing through the multiple sheet. However, even if an attempt is made to return the amount of light passing through the multiple sheet to the level that was obtained before supplying the vapor in between the opposed transparent sheet layers, it is impossible to successfully carry out the attempt in a short period of time since it is not easy to remove the dew condensation generated on the opposed surfaces of the opposed transparent sheet layers. Further, it is impossible to increase the amount of light passing through the multiple sheet to at least the level that was obtained before supplying the vapor in between the opposed transparent sheet layers.